1. Field of the Invention
The present invention relates to foamable organosiloxane compositions. More particularly, this invention relates to foamable organosiloxane compositions exhibiting a high expansion ratio and the absence of incompatible ingredients causing post-cure whitening
2. Background Information
Known methods for preparing elastomeric organosiloxane foams at room temperature include (i) the addition of an organic foaming or blowing agent to a room-temperature-curable organosiloxane composition and (ii) the preparation of an intrinsically foamable room temperature curable organopolysiloxane composition. In the latter method (ii) curing and foaming are simultaneously induced by means of a dehydrogenation reaction between a silanol-containing polyorganosiloxane and an SiH-containing organosilicon compound. This type of reaction is disclosed in Japanese Patent Publication Number Sho 33-9297 [9,297/1958], Japanese Patent Publication Number Sho 44-8755 [8,755/1969], and Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 51-46352 [46,352/1976].
A disadvantage of method (ii) is the low expansion ratio. Specifically, because foaming and curing proceed simultaneously in these methods and therefore cannot be subjected to an independent, deliberate control, good foaming conditions essentially cannot be obtained in the case of molding by foaming in a mold and in the case of injection into a gap or crevice for foaming.
These expansion ratio of foams prepared using method ii can be substantially increased by the addition of diphenylmethylsilanol (DPMS) to the foamable organosiloxane composition. However, because the DPMS and condensates thereof separate out at the surface of the foam after curing, this method suffers from the drawback of products having a grossly impaired external appearance. Another disadvantage of DPMS is its poor compatibility with the other organosiloxane ingredients of the foamable composition, resulting in separation of the DPMS during storage.
The present inventors conducted extensive investigations to solve the aforementioned drawbacks. As a result, they discovered that these drawbacks can be overcome in a single stroke by the addition of a specific polyorganosiloxane to a room-temperature-curable organosiloxane composition whose cure proceeds via dehydrogenation. The present invention was achieved based on this discovery.
One objective of the present invention is to provide a foamable organosiloxane composition that has a high expansion ratio, an excellent moldability, and an excellent storage stability, and that is not subject to post-cure whitening.